This application claims the priority of German Application No. 197 26 720.3, filed Jun. 24, 1997.
The invention relates to a structural member and, more particularly, to a structural member which, in its cross-sectional plane, has at least two closed hollow-section chambers which are produced by rolling forming and which are made of a single sheet metal part, the at least two hollow-section chambers being provided with at least one longitudinal seam.
Strip-shaped structural members, as used in motor vehicle doors as a shock absorbing device, as a bumper reinforcement or as a vehicle body member, are known from German Patent Document DE 195 25 347 C1. That patent document describes a strip-shaped structural member having a sectional part which has in its cross-sectional plane at least two closed chambers produced by sheet metal forming. Between these two closed chambers, an open area is situated which can be closed by reinforcing parts. That invention is based on the fact that the sectional part is produced from a single sheet metal strip. However, an absolutely one-piece production of the strip-shaped structural member cannot be achieved, because that patent document is based on additional reinforcing parts which are required for closing the open area between the two hollow chambers at least in portions. The reinforcing parts required for this purpose must therefore be mounted separately. This does not achieve a produced member which will be in one piece. In addition, the mounting of separate reinforcing parts requires relatively high expenditures and is cost-intensive.
In order to be able to achieve a satisfactory stability of the structural member, it also required in the above-mentioned patent document that intermediate-wall-type spacing parts are arranged in the open area between the hollow chambers of the profile part. These spacing parts incur additional costs and additional manufacturing expenditures.
Another process for manufacturing a motor vehicle bumper is described in U.S. Patent Document U.S. Pat. No. 5,395,036. This patent document describes a process for the one-piece manufacturing of a motor vehicle bumper. However, this construction is not very resistant to bending. The mentioned construction has neither spacing parts nor reinforcing parts, as they are mentioned, for example, in German Patent Document DE 195 25 347 C1. Stability or a high resistance of the construction to bending was not at all important in the case of the process mentioned in the U.S. patent document.
Furthermore, a bumper for motor vehicles which consists of a one-piece sectional member is described in German Patent document DE 31 44 844. In comparison to the U.S. patent document, in this German patent document, a higher stability of the bumper is achieved in that interior webs are provided in the construction. These interior webs cause a corresponding stability. However, the sectional member is not welded as in the case of the other two patent documents but is extruded or drawn. This therefore represents a completely different manufacturing process.
In principle, U.S. Pat. No. 5,340,178 is similar to German Patent Document DE 31 44 844 C2. The U.S. patent document also has interior webs which are used for reinforcing the construction. However, the sectional member is also not welded but rather extruded or drawn.
It is an object of the present invention to provide a structural member made of a low-cost starting material which has a high moment of resistance to bending and which can be produced by means of the manufacturing process by profile rolling which can be carried out at low cost and in a reliable manner with respect to the process.
According to the present invention, this object is achieved by providing a structural member which, in its cross-sectional plane, has at least two closed hollow-section chambers which are produced by rolling forming and which are made of a single sheet metal part, the at least two hollow-section chambers being provided with at least one longitudinal seam. Between the at least two hollow-section chambers at least one intermediate web is provided which forms one piece with the walls of the hollow-section chambers. The at least one intermediate web starts out from the longitudinal seam and is connected on the longitudinal side facing away from the longitudinal seam, with an interior side of the sheet metal part.
As a result of the fact that at least one intermediate web extends between the two hollow-section chambers, the structural member acquires a very high resistance to bending and stability. High load demands can therefore be met. Because of the one-piece construction of the hollow-section chambers and of the intermediate web, the structural member can be produced particularly easily. It therefore requires no unnecessary welding together of separate cross-struts. In particular, the structural member also meets aerodynamic requirements.
Together with the intermediate web, the whole structural component can be produced from one coil width. This permits particularly low-cost production of the structural member. The whole structural member must be connected only at two points by means of conventional processes, for example, by welding. This is advantageously made possible by the special shape of the structural member.
Advantageous further developments and embodiments of the invention are described herein.